LibWeb/DOM: Rename ElementReference to AbstractElement

This isn't some kind of identifier, it's a handle on an actual Element
or PseudoElement.

Libraries/LibWeb/DOM/AbstractElement.cpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2024-2025, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/DOM/AbstractElement.h>
+
+namespace Web::DOM {
+
+AbstractElement::AbstractElement(GC::Ref<Element> element, Optional<CSS::PseudoElement> pseudo_element)
+    : m_element(element)
+    , m_pseudo_element(move(pseudo_element))
+{
+}
+
+void AbstractElement::visit(GC::Cell::Visitor& visitor) const
+{
+    visitor.visit(m_element);
+}
+
+GC::Ptr<Element const> AbstractElement::parent_element() const
+{
+    if (m_pseudo_element.has_value())
+        return m_element;
+    return m_element->parent_element();
+}
+
+GC::Ptr<CSS::ComputedProperties const> AbstractElement::computed_properties() const
+{
+    if (m_pseudo_element.has_value())
+        return m_element->pseudo_element_computed_properties(*m_pseudo_element);
+    return m_element->computed_properties();
+}
+
+CSS::CountersSet& AbstractElement::ensure_counters_set()
+{
+    // FIXME: Handle pseudo-elements
+    return m_element->ensure_counters_set();
+}
+
+void AbstractElement::set_counters_set(OwnPtr<CSS::CountersSet>&& counters_set)
+{
+    // FIXME: Handle pseudo-elements
+    m_element->set_counters_set(move(counters_set));
+}
+
+}